The present invention relates to an operator safety device for a machine, particularly for a printing press.
It is known in the prior art to provide at least some parts of a printing press with covers for protecting an operator against contact with these parts when the machine is in operation. Usually, some of these covers are movable between a closed position in which they cover the corresponding parts of the press and an open position where the covers do not cover the parts and the latter are readily accessible for the operator. However, some of the covers may move to their open positions (for one reason or another) when the press is in operation. In this case, the uncovered parts of the press may constitute a potential danger of accidents.
It is known in the prior art to shut down the press immediately after a cover moves into its open position, by means of a safety device. The safety device includes a plurality of end switches.
The specific task is to protect the operator's narrow passage path between two adjacent presses. The operator's passage path is provided with a plurality of separate covers.
In this case each cover is provided with a switch (i.e., electrical switch) so that once a cover moves in any direction from a predetermined working position the electric circuit system of the machine becomes influenced (see French Pat. No. 2,247,349).
Such an arrangement is very expensive (since it is necessary to provide each cover with a switch and a corresponding electric circuit) and rather unreliable (since the switch becomes actuated even due to a simple misuse of the safety device by the operator, for example due to an inadvertent pressure on the cover by the operator). These shortcomings make the safety device completely inefficient. Besides, breaking of a spring may lead to switching the machine on even when the covers are in their open positions with all undesirable and dangerous consequences.
It is also known to provide a safety device with a so-called interlock switch. The cover of this device is provided with a control cam (fixedly mounted on the cover) which is pivotable about an axis so as to actuate a switch to correspondingly shut down the machine (see British Federation of Master Printers "Safety in Print", 1367, p. 22). Such an arrangement can not be installed in the operator passage path between two adjacent printing presses.